The functions of proteins, nucleic acids and polysaccharides are intimately connected to their chemical composition and the way(s) in which the molecules are arranged in space. Nuclear magnetic resonance spectroscopy has emerged as a powerful method for determining structures of these molecules in solution. However, these molecules can be large and as molecules become larger nmr methods for structural studies begin to falter. The molecular size limitations can often be extended by placement of isotopes of carbon or nitrogen in the molecule of interest, or by examination of fluorine nuclei that have been substituted for hydrogen within the structure. Utilization of these approaches introduces additional complexity into interpretation of nmr results and, depending on the experimental situation, it may be that only by recognizing the underlying theory can reliable interpretations of results be made. This proposal seeks support for continuation of efforts to develop methods for the simulation of nmr experiments by computer that take into account, in general and rigorous ways, the effects of nuclear spin relaxation, r.f. fields, and chemical exchange. These methods can be used directly in the interpretation of experimental results or can be used to compare the results of rigorous treatments to more approximate ones so the accuracy of interpretations of experimental data based on the approximate treatments can be assessed. Although focused on the nmr spectroscopy of fluorine- containing protein systems, the work proposed is directly relevant to nmr studies of biological materials by carbon-13, nitrogen-15, and phosphorus- 31 observations. The project is based on appreciable preliminary work and is timely because many of the effects detected that could lead to errors of interpretation become important at the large magnetic fields that are now available.